SR 25 rifle (Stoner Rifle, model 25) 7.62x51 NATO.
To shoot:
1: Pull the mag in.
2: Cock the weapon using cocking handle (grey part on the left top of the reciver [like in M4 and M16])
3: Pull the trigger (its semi-automatic)
4: If the mag is empty, remove it just by pulling it out.

It shouldn't jamm, but in case of jamms just use cocking handle to remove spent case. And feel free to create sights, bipods etc. and attach them to picatinny rails (if you want to post them, do it as a response to this scene or at least give me credit for original rifle)
Have Phun.
(It propably wont work with algodoo)

Security14
Most parts have 0% appearence, or are covered by rifle skin. If You want to look inside, just change appearence of all parts. And how it works? Its simple blowback operated and uses spring rounds.